This invention relates to various devices for opening and closing valves on internal combustion engines, compressors, and various oil tool field equipment. More specifically it relates to devices which open and close valves in response to rotary motion of a camshaft or crankshaft which allow fluid to enter or escape cylinders which hold a reciprocating piston.
It is well known that the efficiency of an engine or compressor is directly proportional to the rate and volume of intake fluid drawn into the cylinder and exhaust fluid expelled from the cylinder per stroke. The greater the flow rate of intake or exhaust fluid the greater the efficiency of the machine. It has also been recognized in the industry that the efficiency of an engine or compressor can be increased by varying the timing of the intake and exhaust valves with respect to the speed of the engine or compressor and the load placed on the machine. Specifically, the point in time in which the valve opens or closes in relation to the position of the piston in the cylinder and the position of other valves may be adjusted to create optimal flow rates. The optimal flow rates vary depending on how fast the crankshaft is turning and what load is present.
Generally, the prior art teaches that an oblong cam rotating in time with the crankshaft can be used to drive a push rod and rocker arm mechanism to open a valve. A spring is used on the shaft of the valve to close the valve and maintain the rocker arm and push rod in contact with the rotating oblong cam. The prior art also teaches that an oblong cam can be used to drive a valve shaft directly, again relying on a return spring to keep the valve shaft in contact with the cam at all times. In order to vary the timing and the length of time the valve is open, the prior art teaches that the cam diameter or attack angle must be changed responsive to the speed of the crankshaft. Prior art oblong cam driven systems have several limitations. One limitation of all oblong cam driven systems is that the cam can only have a certain limited rate of ascent and descent. Ascent is limited by the mechanical connection between the cam and cam follower; if the ascent rate is too radical a shearing will occur at the cam follower surface. The rate of closure of the valve is controlled by the stiffness of the return spring. At high speeds the valve "float" is problematic. If the cam speed is too high, the strength of the valve return spring cannot close the valve before the cam returns to its open position.
Other valve opening systems are available in the prior art. In one system, disclosed in U.S. Pat. No. 5,078,102 to Matsumoto, the rotating cam is replaced by a stepped cam plate generally perpendicular to the axis of the camshaft. The sliding horizontal cam plate replaces the activating force of a push rod by directly forcing an opposing rocker arm up, thus activating the valve. Timing of an engine equipped with this valve opening system is changed by mechanically lengthening or shorting various mechanical control elements which change the relationship of the cam surface in response to crankshaft's angular position.
Stepped cam plate systems have several limitations. First, they are difficult to implement on existing engines because the travel of the step cam plate is perpendicular to the rotational axis of the crankshaft and camshaft. The system also is difficult to use in retrofitting existing engines. Finally, the timing variation is accomplished by a complex hydraulic system which is difficult to implement and maintain.
U.S. Pat. No. RE. 30,188 to Predhome, Jr. discloses a different system for replacing an oblong rotating cam. This device implements a desmodromic cam and cam follower to convert rotation of a camshaft to rotary oscillation of the cam follower and in turn into activation of the valves. While novel, the system is difficult to use in retrofitting existing engines and retains the need of return springs to close the valves.